It is often necessary to run a tubing string down into a wellbore which has a bottomhole pressure of several thousand pounds. Sometimes the tubing string includes a packer which packs off the lower borehole annulus from the upper annulus as seen for example in my previously issued U.S. Pats. No. 3,812,911; 3,871,448; 3,912,013; 3,931,855; 3,990,507; and 4,009,757.
Mechanically actuated vent assemblies are often difficult to manipulate for the reason that the bottomhole pressure causes the pressure differential across the tubing string to often amount to several thousand psi, and therefore, an enormous amount of pressure is exerted through the vent ports and against the sliding element associated with the vent assembly. The difficulty often reaches a magnitude which appears insurmountable and the technicians sometimes find themselves resorting to the use of a knocker, or jar, and other impact type tools in order to force the sliding sleeve to move into the open position.
In deep wells having an extremely large bottomhole pressure, the rapid opening of the sliding sleeve causes a sudden and tremendous inrush of fluids to occur. The fluids enter the vent assembly and flow up the tubing string with sufficient violence to simulate a wild well, and it is very distressing to attempt to bring such a well under control, especially when some sort of trouble is precipitated by the energy dissipated by the sudden onrush of the extremely high pressure well fluids.
It is costly to remove all of the tubing string and attendant equipment from a deep well as is necessary when the vent assembly refuses to be actuated to the open position. It is furthermore costly to be forced to shut-in a well as a result of the sudden onrush of fluids precipitating damage to the tool string or wellhead. Accordingly, it is desirable to be able to run an improved vent assembly downhole into a high pressure borehole and to subsequently actuate the vent assembly in such a manner to slowly equalize the pressure before opening the well to flow. Such a desirable expedient would eliminate the potentiality of the above damage and thereby avoid the necessity of removing the entire tool string from the borehole; and furthermore, would avoid the destructive onrush of high pressure fluids through the various piping and valves associated with the completion of the borehole. A vent assembly having the above desirable attributes is the subject of the present invention.